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Many studies have demonstrated that HDL, the "good" cholesterol, ferries LDL, the "bad" cholesterol, out of the bloodstream. High doses of vitamin B-3, known as niacin, raise HDL. Therefore, taking a high dose of niacin should raise HDL and protect against atherosclerosis, the buildup of waxy plaque that clogs arteries and promotes heart disease.

As logical as that may sound, a recent study failed to find any benefit at all to a high dose of Niaspan, a prescription-only form of niacin, in people who already were taking simvastatin (a statin drug sold as Zocor) to reduce their bad LDL.

The results were so disappointing that the sponsor of the study, the National Institutes of Health, halted it early.

So what's a doctor to do?

Just 2,000 milligrams a day of plain niacin reduces the bad LDL cholesterol as well as the blood fats known as triglycerides. But even 500 milligrams of niacin is enough to cause skin flushing and itching that last for 10 or 15 minutes, and patients need about 2,000 milligrams per day to obtain the maximum benefit. That's too much discomfort for many people.

But in a recent study of 3,400 people with heart disease, those who took niacin along with statins to reduce their cholesterol did no better than those who took statins alone. In fact, those who took niacin experienced a slightly greater number of strokes.

Why, despite several studies showing that niacin protects against heart attacks and strokes, did niacin fail to produce any benefit this time?

Dr. Stanley L. Hazen of the Cleveland Clinic, who is conducting an intensive study of the effect of HDL cholesterol on atherosclerosis, suspects the answer is buried in the details of the recent study.

"I think the design of the study was a little unfortunate," he said.

First, all 3,400 patients in the study were taking a statin, which suppresses the production of cholesterol in the liver. Some also were taking ezetimibe, sold as Zetia, which inhibits cholesterol absorption by the intestines. Then half of the patients also took prescription Niaspan, formulated to reduce the flushing produced by the vitamin.

"The problem is that they allowed physicians to prescribe additional statin or ezetimibe to further reduce LDL," Hazen said. "As a result, both groups ended up achieving the same LDL levels, so you're really comparing a lower dose statin plus niacin to either a higher dose of statin or a higher dose of statin plus ezetimibe. It's complicated, but it looks like the levels of LDL were very low in everyone, and no significant improvement was seen in those who took niacin as well."

What that suggests to Hazen is that once the LDL is reduced to a very low level — around 70 milligrams per deciliter of blood — niacin provides no additional benefit.

"There's a lot of very good data that argues niacin by itself reduces heart attack, stroke and death," Hazen said. "The way this trial was designed minimizes the potential benefit of niacin. Therefore, I don't think you can look at this and say that niacin is an inappropriate drug to use."

He and his colleagues will continue to prescribe niacin for their patients at risk of heart attack and stroke, he said. "We haven't changed our practice at all," he said. "We're waiting for other trials."

They also will continue to prescribe statins first in an effort to reduce the bad LDL cholesterol.

"For those patients who can't take statins — who get muscle aches or some other problem from the drug — then niacin is still an excellent alternative. The only question is, if patients achieve the goal of getting their LDL below 70, but still have low HDL cholesterol, does adding niacin provide any benefit? Until we actually see the complete trial results, I'm not convinced we can say."

So should you take niacin or not? And what about the "flush-free," "no-flush" and "timed release" versions?

Here's what Hazen says: If your LDL is too high and you can't tolerate statins, then take niacin, but only plain niacin, also known as nicotinic acid. "This so-called no-flush niacin should never be used," he said. "It's totally useless. It has no impact on lipoprotein levels. The label needs to say niacin and vitamin B-3, not this inositol hexaniacinate."

But if you're taking niacin to raise your HDL thinking it might help remove LDL, you may be wasting your time.

The main message, according to Hazen, is that for people who need to lower their LDL cholesterol, even if they're already on a statin, taking niacin is a perfectly viable option. "We have gotten calls," he said, "from patients asking, 'Should I stop taking niacin?' We tell them, do not stop niacin. In our clinic we are still aggressively using niacin to help patients achieve their LDL goals.

"We just don't have enough information to say it's not helpful. I think we've been over-analyzing the results of this new study without having all the information."

Tom Valeo writes frequently about health matters. He can be reached at tom.valeo@gmail.com.